The present invention is directed towards the preparation of a latex having high tensile strength without a loss in elongation. This improvement in physical properties results in a latex suitable as an adhesive having high shear adhesion without a loss of peel adhesion.
In the adhesive industry there is a great desire for adhesives having a balance of shear and peel adhesion. Unfortunately, shear adhesion is contributed by the tensile property of the latex film and peel adhesion is contributed by the elongation property of the latex film. Tensile and elongation are antagonistic properties and; therefore, increasing one tends to decrease the other. In order to cope with this problem, various methods for preparing latexes have been attempted.
One method, and perhaps most common, is to copolymerize various monomers to obtain the benefit of the individual monomer components. Another polymerization method is to stage the addition of monomers to form a structured latex particle having diverse properties. While either method has produced latexes having properties acceptable for adhesives, especially pressure sensitive adhesives, it is still desirable to increase either shear or peel adhesion without sacrificing the other.